The purpose of this Phase I SBIR proposal is to develop a 3 micron stabilized microbubble for tumor detection when used in conjunction with ultrasound. This proposal builds on a microbubble technology that originated in 1976 by the PI and has continued since that time. Gelatin encapsulated microbubbles adhere to abnormal vessel walls. Because bubbles act as ultrasonic reflectors, small quantities of microbubbles can be visualized with clinical ultrasound, and it is hoped that they will be effective in detecting small tumors. Such bubbles act as site-specific tumor markers when they adhere to tumor vessel walls for up to 15 minutes, but microbubbles entering normal tissue dissolve and clear in minutes. In order to provide the clinician with some control over the microbubbles, a biocompatible iron oxide, which is capable of being displaced by a magnet, will be added to the bubble wall. Thus, using ultrasound, the clinician can observe the bubble agents while under magnetic guidance in order to concentrate them in the target area. The primary goal of the proposed Phase I effort is to develop a bubble generator capable of producing 3 micron gelatin encapsulated microbubbles. Phase II activities will be aimed at quantification and optimization of the technique in vivo with implanted and spontaneous tumors.